The lubrication of transmission components and the cooling of components, in particular the shift elements of automatic transmissions of motor vehicles, is typically controlled in a manner dependent on torque and rotational speed, in order to provide the quantity of oil for lubricating and cooling transmission components that is in line with demand as much as possible. Due to the viscous properties of cooling oil, lower volume flows arise at low temperatures than at high temperatures, such that the quantity of oil supplied depends on temperature.
Strict fuel economy and emissions standards have resulted in the need to even further optimize the efficiency of automatic transmissions. Thereby, drag torque in particular is to be reduced in the range relevant for the consumption cycle. The NEDC (New European Driving Cycle) consumption cycle takes place in a limited range of operation, namely in the lower temperature range with moderate transmission loads.
DE 4342961 C1 discloses an arrangement for controlling the temperature of a hydraulic operating medium (working oil) for an automatically shifting transmission and a hydrodynamic torque converter with a converter feed line for the operating medium, for which a radiator for the heat dissipation of the operating medium with a radiator return line leading to the transmission and a control valve working as a function of the temperature of the operating medium are used, and a converter return line outgoing from the torque converter, a radiator supply line leading to the radiator and a line for the control valve directly connected to the transmission are attached, which, at temperatures lower than a lower-temperature phase comprising a threshold value, it is both the case that the converter return line is shut off with respect to the radiator supply line and the line directly connected to the transmission is connected to a first of the lines attached to the control valve, while, at temperatures higher than an upper-temperature phase comprising the threshold value, it is both the case that the converter return line is connected to the radiator supply line and the line directly connected to the transmission is connected to a second of the lines attached to the control valve. It is thereby provided that the converter supply line is also connected to the control valve, that, in the lower-temperature phase, it is both the case that the converter return line is connected to the converter supply line and the line directly connected to the transmission is connected to the radiator supply line, and that, in the upper-temperature phase, the converter supply line is connected to the line directly connected to the transmission, such that a temperature-dependent radiator flow control is realized.